Clips with Elastic

Modern railway systems rely on a collection of precisely engineered components working in unison to ensure safety and stability. Among the most critical of these are the clips with elastic properties, which form the heart of the rail fastening system. Unlike rigid spikes, these advanced fasteners are designed to apply a continuous, dynamic clamping force to the base of the rail. This holds it securely to the sleeper, maintains precise track gauge, absorbs vibrations, and controls the longitudinal forces known as rail creep. This technical guide explores the specifications, primary types, and material characteristics of these essential railway components.

Specifications and Performance of Clips with Elastic

Key technical specifications define the performance of an elastic rail clip. These metrics determine the clip’s suitability for a given application, from a light transit line to a heavy-haul freight corridor. The primary function of all clips with elastic is to provide a consistent clamping force.

• Toe Load (Clamping Force): This is the most critical specification. It is the downward force exerted by the tip (or “toe”) of the clip onto the rail base. Toe load is measured in kilonewtons (kN) and typically ranges from 8 kN to 12 kN per clip, depending on the system. A sufficient toe load is required to prevent the rail from moving vertically or rotating under load.
• Fatigue Life: Rail clips are subjected to millions of load cycles as trains pass. They must be designed to withstand this repetitive stress without failing. The fatigue life is a measure of how many cycles a clip can endure before a fatigue crack is likely to form, often specified to be in the range of 3 to 5 million cycles.
• Material and Hardness: The vast majority of clips with elastic are forged from high-quality spring steel, typically a silico-manganese alloy like 60Si2MnA or a similar grade. The steel is heat-treated to achieve a specific hardness (usually in the range of 42-48 HRC) that provides the necessary spring properties without becoming brittle.

Types of Clips with Elastic and Their Dimensions

Several distinct designs for elastic clips have become industry standards, each with unique characteristics and installation methods. Manufacturers precisely control their dimensions to ensure they fit the rail profile and fastening assembly correctly.

1. E-Type Clips

The E-type clip is one of the most recognizable and widely used elastic fasteners globally. It features a distinct ‘e’ shape and is driven horizontally into a cast iron shoulder that is embedded in a concrete sleeper.

• Design: The clip functions as a spring lever. When workers drive it into the shoulder, its middle leg presses against the cast shoulder, forcing the upper and lower toes to deflect and clamp onto the rail flange.
• Common Models & Dimensions: E-type clips come in various sizes, such as the E1609, E1809, E2007, and E2055. The number often relates to the diameter of the steel bar used to make the clip (e.g., E1809 uses an 18mm bar). Their dimensions are precisely matched to the specific rail profile and shoulder type they are designed for.
• Application: E-type clips are extremely versatile and are used on mainline tracks, transit systems, and turnouts worldwide. They offer excellent clamping force and are relatively easy to install and maintain.

2. SKL (Spannklemme) Tension Clips

German engineers developed the SKL, or tension clamp system, and many European and Asian railways favor this design. Unlike the E-type clip, a screw spike holds the SKL clip in place.

• Design: The SKL clip has a distinctive “W” shape. Workers place it over the rail flange and tighten a threaded T-bolt or screw spike, forcing the center loop of the clip downward. This deflection generates the clamping force at the two toes of the clip.
• Common Models: The SKL system has evolved through several iterations, including the SKL-1, SKL-3, SKL-12, and SKL-14. Each generation offers improvements in performance and clamping force. The SKL-14 is a common modern standard.
• Application: SKL systems are known for their high clamping force and excellent resistance to rail creep. They are widely used on high-speed and heavy-haul lines. The threaded fastening allows for easy adjustment and re-tightening if necessary.

3. PR-Type Clips and Other Variants

The PR-type clip is another variation that functions similarly to the E-type clip but has a slightly different geometry. It is also driven into a shoulder to generate its clamping force.

• Design: The PR-clip has a more compact, angular design than the E-type. It is known for its high fatigue resistance and is used in various mainline applications.
• Nabla Clip System: The Nabla clip features a blade-like spring that is secured by a bolt. Tightening the bolt causes the blade to flex and apply a downward force on the rail. Engineers recognize this system for its excellent vibration damping properties.

Material Grades and Compatibility with Rail Profiles

The effectiveness of any elastic clip depends entirely on its compatibility with the specific rail profile it must secure. Engineers design the clip’s dimensions to match the geometry of the rail base.

The Importance of Base Width and Flange Angle

The most critical dimensions for compatibility are the rail’s base width and the angle of its top flange. A clip designed for a UIC60 rail (150 mm base width) will not function correctly on a 115RE rail (139.7 mm base width).

• Incorrect Fit: If a clip is used on a rail base that is too narrow, it will not be sufficiently deflected and will fail to generate the required toe load. If the base is too wide, it can overstress the clip, causing premature failure, or prevent the clip from seating properly in the shoulder.
• System Integration: The complete fastening assembly, including the clip, insulator, pad, and shoulder, is designed as an integrated system for a specific rail profile (e.g., 136RE, UIC60, 52kg). Using components from different systems or for different rail sections is a critical safety violation that can lead to gauge widening and potential derailment.

The chart below shows examples of rail profiles and the types of clips with elastic that are commonly paired with them.